A method for reducing particulate emissions

ABSTRACT

A method for reducing particulate emissions from a direct injection spark-ignition engine, wherein the method comprises fuelling the engine with a gasoline composition, wherein the gasoline composition comprises a hydrocarbon base fuel comprising not greater than 5% v aromatics of at least 9 carbon atoms, based on the base fuel, a T90 of up to 150° C. and a final boiling point not greater than 190° C.

FIELD OF THE INVENTION

This invention relates to a method for reducing particulate emissions from a direct injection spark-ignition engine.

BACKGROUND OF THE INVENTION

There is increasing concern about the environmental effects of particulate emissions from spark-ignition combustion engines, particularly from direct injection spark-ignition engines. This has resulted in a growing demand for motor vehicles that operate with reduced particulate emissions.

Current hydrocarbon fuels developed for spark-ignition combustion engines may not be optimised or indeed beneficial for direct injection spark-igntion engines, particularly when it comes to levels of particulate emissions. It would therefore be desirable to find ways of reducing the particulate emissions from the operation of a direct-injection spark ignition engine.

WO2004/113476 discloses gasoline compositions meeting certain parameters whose use as a fuel in a spark ignition engine results in improved stability of engine crank case lubricant. However, there is no mention in this document of the use of such a fuel for providing reduced particulate emissions in a direct-injection spark ignition engine.

SUMMARY OF THE INVENTION

According to the present invention there is provided a method for reducing particulate emissions from a direct injection spark-ignition engine, wherein the method comprises fuelling the engine with a gasoline composition, wherein the gasoline composition comprises a hydrocarbon base fuel comprising not greater than 5% v aromatics of at least 9 carbon atoms, based on the base fuel, a T90 of up to 150° C. and a final boiling point not greater than 190° C.

According to the present invention there is further provided a use of a gasoline composition for reducing particulate emissions from a direct injection spark-ignition engine, wherein the gasoline composition comprises a hydrocarbon base fuel comprising not greater than 5% v aromatics of at least 9 carbon atoms, based on the base fuel, a T90 of less than 150° C. and a final boiling point not greater than 190° C.

It has surprisingly been found that by selecting a gasoline composition meeting certain parameters the particulate emissions from a direct injection spark-igntion engine are reduced.

DETAILED DESCRIPTION OF THE INVENTION

Low C9+ aromatics content together with a T90 of less than 150° C. and a final boiling point of not greater than 190° C. are believed to be key parameters in achieving reduced particulate emissions from a direct-injection spark ignition internal combustion engines fuelled by gasoline compositions of the present invention.

By “not greater than 5% v aromatics of at least 9 carbon atoms” is meant that the hydrocarbon base fuel contains amounts of aromatics having 9 carbon atoms or more, respectively in the range 0 to 5% v, based on the base fuel.

The uses and methods of the present invention may be used to achieve any degree of reduction in particulate emissions from a direct-injection spark ignition engine, including reduction to zero (i.e. eliminating particulate emissions). It may be used for the purpose of achieving a desired target level of particulate emissions. The method and use herein preferably achieves a 5% reduction or more in particulate emissions from a direct injection spark ignition engine, more preferably a 10% reduction or more in particulate emissions from a direct injection spark ignition engine, even more preferably a 15% reduction or more in particulate emissions from a direct injection spark ignition engine, and especially a 30% reduction or more in from a direct injection spark ignition engine, compared with the use of a gasoline fuel composition having a final boiling point of greater than 190° C., a T90 of 150° C. or more and comprising greater than 5v % of aromatics having 9 carbon atoms or more.

Any suitable method for measuring particulate emissions from direct injection spark ignition engines can be used herein. An example of a suitable method for measuring particulate emissions can be found in the following SAE paper: SAE 2010-01-2115 published 25th October 2010 which measures the reduction of particulate emissions by a decrease in PM index of the gasoline composition. Gasoline compositions suitable for use in the present invention preferably have a PM index as measured according to the test method disclosed in SAE 2010-01-2115 of 1.0 or less, more preferably 0.95 or less, even more preferably 0.9 or less.

Gasolines contain mixtures of hydrocarbons, the optimal boiling ranges and distillation curves thereof varying according to climate and season of the year. The hydrocarbons in a gasoline as defined above may conveniently be derived in known manner from straight-run gasoline, synthetically-produced aromatic hydrocarbon mixtures, thermally or catalytically cracked hydrocarbons, hydrocracked petroleum fractions or catalytically reformed hydrocarbons and mixtures of these. Oxygenates (both fossil- or bio-sourced) may be incorporated in gasolines, and these include alcohols (such as methanol, ethanol, isopropanol, tert.butanol and isobutanol) and ethers, preferably ethers containing 5 or more carbon atoms per molecule, e.g. methyl tert.butyl ether (MTBE) or ethyl tert.butyl ether (ETBE). The amount of oxygenates present in the fuel composition is dependent upon the prevailing fuel specification for oxygenate species. For example, the EN228 specification sets a maximum oxygen content of 3.73% oxygen by mass and therefore the level of oxygenate content has to be adjusted to comply with this.

It is preferred to avoid inclusion of tert.butanol or MTBE. Accordingly, preferred gasoline compositions of the present invention contain 0 to 10% by volume of at least one oxygenate selected from methanol, ethanol, isopropanol and isobutanol.

Theoretical modelling has suggested that inclusion of ethanol in gasoline compositions of the present invention will further enhance stability of engine lubricant, particularly under cooler engine operating conditions. Accordingly, it is preferred that gasoline compositions of the present invention contain up to 10% by volume of ethanol, preferably 2 to 10% v, more preferably 4 to 10% v, e.g. 5 to 10% v ethanol.

Other oxygenates that may be included in the gasoline compositions herein include diethyl carbonate (DEC) which is made catalytically from ethanol and CO2, esters such as ethyl acetate and ketone such as methyl ethyl ketone.

Oxygenates can help to reduce PN emissions through chemical means.

Gasoline compositions according to the present invention are advantageously lead-free (unleaded), and this may be required by law. Where permitted, lead-free anti-knock compounds and/or valve-seat recession protectant compounds (e.g. known potassium salts, sodium salts or phosphorus compounds) may be present.

The octane level can be defined by RON, MON or the anti-knock index (Aki) ((RON+MON)/2). If RON is specified, it will generally be greater than 92. If anti-knock index is specified it will generally be above 85.

Modern gasolines are inherently low-sulphur fuels, e.g. containing less than 200 ppmw sulphur, preferably not greater than 50 ppmw sulphur.

Hydrocarbon base fuels as defined above may conveniently be prepared in known manner by blending suitable hydrocarbon, e.g. refinery, streams in order to meet the defined parameters, as will readily be understood by those skilled in the art. Olefin content may be boosted by inclusion of olefin-rich refinery streams and/or by addition of synthetic components such as diisobutylene, in any relative proportions.

Diisobutylene, also known as 2,4,4-trimethyl-1-pentene (Sigma-Aldrich Fine Chemicals), is typically a mixture of isomers (2,4,4-trimethyl-1-pentene and 2,4,4-trimethyl-2-pentene) prepared by heating the sulphuric acid extract of isobutylene from a butene isomer separation process to about 90° C. As described in Kirk-Othmer, “Encyclopedia of Chemical Technology”, 4^(th) Ed. Vol. 4, Page 725, yield is typically 90%, of a mixture of 80% dimers and 20% trimers.

Gasoline compositions as defined above may variously include one or more additives such as anti-oxidants, corrosion inhibitors, ashless detergents, dehazers, dyes, lubricity improvers and synthetic or mineral oil carrier fluids. Examples of suitable such additives are described generally in U.S. Pat. No. 5,855,629 and DE-A-19955651.

Additive components can be added separately to the gasoline or can be blended with one or more diluents, forming an additive concentrate, and together added to base fuel.

A preferred gasoline composition for use in the method of the present invention comprises one or more antioxidants in order to improve the oxidative stability of the gasoline composition. Any antioxidant additive which is suitable for use in a gasoline composition can be used herein. A preferred anti-oxidant for use herein is a hindered phenol, for example BHT (butylated hydroxy toluene). It is preferred that the gasoline composition comprises from 10 ppmw to 100 ppmw of antioxidant.

Non-oxygenated high octane components that can be bio-sourced and which suitable for use herein include iso-butylenes or iso-octenes, iso-octane, triptane and iso-pentenes. These non-oxygenated high octane compounds help to reduce PN emissions through ignition and combustion optimization.

Preferred gasoline compositions used in the method of the present invention have one or more of the following features:—

(i) the hydrocarbon base fuel contains at least 10% v olefins, (ii) the hydrocarbon base fuel contains at least 12% v olefins, (iii) the hydrocarbon base fuel contains at least 13% v olefins, (iv) the hydrocarbon base fuel contains up to 20% v olefins, (v) the hydrocarbon base fuel contains up to 18% v olefins, (vi) the base fuel has initial boiling point (IBP) of at least 28° C., (vii) the base fuel has IBP of at least 30° C., (viii) the base fuel has IBP up to 42° C., (ix) the base fuel has IBP up to 40° C., (x) the base fuel has T₁₀ of at least 42° C., (xi) the base fuel has T₁₀ of at least 45° C., (xii) the base fuel has T₁₀ of at least 46° C., (xiii) the base fuel has T₁₀ up to 58° C., (xiv) the base fuel has T₁₀ up to 57° C., (xv) the base fuel has T₁₀ up to 56° C., (xvi) the base fuel has T₁₀ of at least 80° C., (xvii) the base fuel has T₁₀ of at least 82° C., (xviii) the base fuel has T₁₀ of at least 83° C., (xix) the base fuel has T₁₀ up to 105° C., (xx) the base fuel has T₁₀ up to 104° C., (xxi) the base fuel has T₁₀ up to 103° C., (xxii) the base fuel has T₉₀ at least 135° C., (xxiii) the base fuel has T₉₀ of at least 140° C., (xxii) the base fuel has T₉₀ of at least 142° C., (xxv) the base fuel has T₉₀ up to 150° C., (xxvi) the base fuel has T₉₀ up to 145° C., (xxvii) the base fuel has 1₉₀ up to 143° C., (xxviii) the base fuel has FBP not greater than 190° C., (xxix) the base fuel has FBP not greater than 185° C., (xxx) the base fuel has FBP not greater than 180° C., (xxxi) the base fuel has FBP not greater than 175° C., (xxxii) the base fuel has FBP not greater than 172° C., (xxxiii) the base fuel has FBP of at least 165° C., and (xxxiv) the base fuel has FBP of at least 168° C.

Examples of preferred combinations of the above features include (i) and (iv); (ii) and (v); (iii) and (v); (vi), (viii), (x), (xii), (xvi), (xix), (xxii), (xxv) and (xxix); (vii), (ix), (xi), (xiv), (xvii), (xx), (xxiii), (x×v) and (x×x); and (vii), (ix), (xii), (xv), (xviii), (xxi), (xxiv), (xxvii), (xxxiii) and (xxxiv).

Use of the gasoline composition described herein can give one of a number of benefits in addition to reducing particulate emissions in a direct injection spark-ignition engine. These benefits include reduced frequency of oil changes, reduced engine wear, e.g. engine bearing wear, engine component wear (e.g. camshaft and piston crank wear), improved acceleration performance, higher maximum power output, and/or improved fuel economy.

The invention will be understood from the following illustrative examples, in which, unless indicated otherwise, temperatures are in degrees Celsius and parts, percentages and ratios are by volume. Those skilled in the art will readily appreciate that the various fuels were prepared in known manner from known refinery streams and are thus readily reproducible from a knowledge of the composition parameters given.

In the examples, particulate matter emissions tests on gasoline compositions in direct injection spark ignition engines fuelled by test fuels were effected using the following procedure.

Examples

The fuel compositions of Examples 1-4 are shown in Table 2 below. Each of these are prepared from the gasoline base fuel having the properties set out in Table 1 below, and for each example the v % of heavy aromatics (aromatics having at least 10 carbon atoms) is adjusted such that it contains an amount of heavy aromatics (C9+) as specified in Table 2 below. Thus, Example 1 contains 0% v heavy aromatics, Example 2 contains 4% v heavy aromatics, Example 3 contains 8% v heavy aromatics and Example 4 contains 12% v heavy aromatics.

TABLE 1 (Properties of Base Fuel) IBP (° C.) 31.9 T10 (° C.) 47.3 T50 (° C.) 102.0 T90 (° C.) 142.7 FBP (° C.) 179.3 RVP (kPa) 65.1 RON 95.3 MON 82.9 Aki ((RON + MON)/2) 89.1 Sensitivity (RON − MON) 12.43 Paraffins (% v) 49.7 Olefins (% v) 14.3 Aromatics (% v) 32.7 PM index 0.81 C9 aromatics (% v) 2.65 C10 aromatics (% v) 0.26 C11 aromatics (% v) 0.00 C12 aromatics (% v) 0

The fuel compositions in Table 2 are subjected to the particulate matter emissions test described in SAE Paper 2010-01-2115 in order to measure their PN index. Results are shown in Table 2 below.

TABLE 2 Example: 1 2 3 4 % v heavy (C9+) 0% v 4% v 8% v 12% v aromatics IBP (° C.)) 32.9 32.65 32.95 33.27 T10 (° C.) 49.0 48.2 49.32 50.50 T50 (° C.) 100.1 102.5 106.11 109.90 T90 (° C.) 134.7 144.1 148.52 153.88 FBP 152.9 189.6 201.90 211.72 RVP (kPa) 66.15 68.58 66.51 64.42 RON 96.7 96.0 96.51 97.12 MON 82.8 82.7 83.08 83.49 Aki 89.8 89.3 89.8 90.3 Sensitivity 13.9 13.3 13.4 13.6 Paraffins (% v) 44.9 44.5 42.66 40.81 Olefins (% v) 20.3 20.2 19.31 18.48 Aromatics (% v) 32.50 33.07 35.86 38.63 PM Index 0.75 0.89 1.08 1.315 C9 aromatics (% v) 0 3.00 5.98 8.44 C10 aromatics 0 0.70 1.25 2.30 (% v) C11 aromatics 0 0 (% v) C12 aromatics 0 0.30 0.77 1.24 (% v) C9+ aromatics 0 4.00 8.00 11.98 (% v)

DISCUSSION

As can be seen from the results in Table 2 above, the gasoline compositions having a hydrocarbon base fuel comprising not greater than 5% v aromatics of at least 9 carbon atoms, based on the base fuel, a T90 of less than 150° C. and a final boiling point not greater than 190° C., provide a greater reduction in particulate emissions (as measured by a decrease in PM index). 

1. A method for reducing particulate emissions from a direct injection spark-ignition engine, wherein the method comprises fuelling the engine with a gasoline composition, wherein the gasoline composition comprises a hydrocarbon base fuel comprising not greater than 5% v aromatics of at least 9 carbon atoms, based on the base fuel, a T90 of up to 150° C. and a final boiling point not greater than 190° C.
 2. The method of claim 1 wherein the hydrocarbon base fuel has a final boiling point of not greater than 180° C.
 3. The method of claim 1 or 2 wherein the reduction of particulate emissions is measured by a decrease in PM index (SAE Technical Paper 2010-01-2115) of the gasoline composition.
 4. The method of any of claims 1 to 3 wherein the gasoline composition has a PM index of 1.0 or less.
 5. The method of any of claims 1 to 4 wherein the gasoline composition contains 0 to 10% v of at least one oxygenate selected from methanol, ethanol, isopropanol and isobutanol, diethylcarbonate.
 6. The method of any of claims 1 to 5 wherein the hydrocarbon base fuel contains 10 to 20% v olefins.
 7. The method of any of claims 1 to 6 wherein the hydrocarbon base fuel contains 12 to 18% v olefins.
 8. The method of any of claims 1 to 7 wherein the hydrocarbon base fuel contains not greater than 5% v olefins of at least 10 carbon atoms, based on the base fuel.
 9. The method of any of claims 1 to 8 wherein the base fuel has initial boiling point in the range 30 to 40° C., T10 in the range 45 to 57° C., T50 in the range 82 to 104° C., T90 in the range 140 to 150° C.
 10. The method of any of claims 1 to 9 wherein the fuel composition comprises one or more antioxidants.
 11. Use of a gasoline composition for reducing particulate emissions from a direct injection spark-ignition engine, wherein the gasoline composition comprises a hydrocarbon base fuel comprising not greater than 5% v aromatics of at least 9 carbon atoms, based on the base fuel, a T90 of up to 150° C. and a final boiling point not greater than 190° C. 